Method for producing caro&#39;s acid

ABSTRACT

This invention relates to a process for producing Caro&#39;s acid by reaction of at least 85% by weight sulfuric acid and at least 50% by weight hydrogen peroxide wherein the sulfuric acid and hydrogen peroxide are fed through separate feed lines into a funneling zone open to the atmosphere, the feed lines having air gaps between their ends and the funneling zone; passing said hydrogen peroxide and sulfuric acid by gravity flow from said funneling zone into one end of a reaction zone whose size permits a pressure drop which is at least 8 times the theoretical pressure drop for such reaction zone and removing a mixture containing Caro&#39;s acid from the exit end of the reaction zone.

This is a continuation-in-part of U.S. application Ser. No. 08/283,348,filed Aug. 1, 1994.

FIELD OF THE INVENTION

The invention is in the field of producing Caro's acid by reaction ofhydrogen peroxide and sulfuric acid in a controlled and effectivemanner.

DESCRIPTION OF PRIOR ART

Caro's acid, which is peroxymonosulfuric acid, is a strong oxidizingcompound which has been suggested for use in many applications includingpurification of cyanide-containing effluents by conversion of theircyanides into non-toxic derivatives. Caro's acid is usually produced byreacting together concentrated sulfuric acid (85% to 98% by weight H₂SO₄) with concentrated hydrogen peroxide (50% to 90% by weight H₂ O₂) toproduce an equilibrium mixture of Caro's acid containingperoxymonosulfuric acid (H₂ SO₅), sulfuric acid and hydrogen peroxide.However, since the Caro's acid is not stable for long periods it must bemade and immediately used on site or quickly cooled and stored atrefrigerated temperatures. In general, the Caro's acid is manufacturedon site as needed and in just the amounts required for the specifiedapplication without the necessity of having to store any excess amounts.

one procedure for producing Caro's acid is set forth in U.S. Pat. No.3,900,555 by using an apparatus described in U.S. Pat. No. 3,939,072 formixing the sulfuric acid and hydrogen peroxide and cooling the mixturewith a water-cooled jacket to prevent overheating of the reactants andpremature decomposition of the monoperoxysulfuric acid product. Thesepatents teach the use of the monoperoxysulfuric acid product fortreating waste aqueous effluents from an electroplating plant containingcyanide ions while simultaneously adding an alkali in amounts suitablefor neutralizing the added acid. This assures that the pH of the treatedsolution in maintained at a specified alkaline value, normally pH 9, byneutralizing any acidity resulting from the added acid.

Another procedure is set forth in U.S. Pat. No. 4,915,849 wherein theCaro's acid is used to treat cyanide-containing effluents from anore-processing plant. The Caro's acid is manufactured by reactingsulfuric acid with hydrogen peroxide in proportions corresponding tobetween 0.01 and 0.5 moles of sulfuric acid per mole of hydrogenperoxide. The resulting acid is then added to the cyanide-containingeffluent simultaneous with aqueous lime or sodium hydroxide mixtures inorder to maintain the effluent at the preferred pH of between 9.5 and11.5.

Still another procedure is set forth in PCT Publication No. WO 92/07791,a published patent application of Lane et al, which teaches productionof peroxymonosulfuric acid by introducing a hydrogen peroxide solutioninto a stream of sulfuric acid flowing through a reaction chamber, theH₂ O₂ introduction being intermediate the sulfuric acid inlet and thereaction mixture outlet. Both the hydrogen peroxide solution andsulfuric acid are introduced under pressure into the closed tubularreaction chamber of the invention. In the reaction chamber, thethrough-put per minute of the reaction chamber is at least about 20times its internal volume measured between the inlet for the hydrogenperoxide and the outlet.

In carrying out the production of Caro's acid in industrialapplications, two problems have arisen in the scale-up of the Caro'sacid generating unit to commercial proportions. The first problem is theprotection of a large amount of hydrogen peroxide in storage tanks, usedto feed the Caro's acid producing generator, from possiblecontamination. The need to prevent contamination of this large hydrogenperoxide source from either Caro's acid, sulfuric acid, or other suchimpurities is critical to the safe containment and use of the hydrogenperoxide. The second problem is to control the Caro's acid reaction sothat the Caro's acid is formed efficiently with maximum use of thehydrogen peroxide reagent and without having the hot reaction mixtureformed during the reaction go out of control and overflow or rupture thereaction chamber.

With respect to the first problem, it has been the custom in theindustry to isolate the storage tank of peroxide from the reactor whereCaro's acid is produced by means of an intermediate tank (sometimescalled a "break" tank) to interrupt the stored hydrogen peroxide sourcefrom the line delivering hydrogen peroxide to the Caro's acid generator.The peroxide from the storage tank is passed by pump means or by gravityinto the top of an intermediate tank to a given level in theintermediate tank without requiring a direct liquid connection betweenthe peroxide in the intermediate tank and the line flowing from thestorage tank. This assures that any possible contamination which may besucked back from the Caro's acid generator into the intermediate tankwill not be able to flow into the hydrogen peroxide storage tank.

The second problem arises because the reaction of sulfuric acid andhydrogen peroxide is an exothermic reaction and some hydrogen peroxidedecomposes to form large amounts of gas which may cause pressure buildup capable of rupturing the reactor or causing the reagents to overflow.This may cause the hot reaction mixture to go out of control with thewaste of both sulfuric acid and hydrogen peroxide and further, if nobreak tank is used, may become a possible source of contamination of thehydrogen peroxide storage tank if it backs up into the hydrogen peroxideline connecting the hydrogen peroxide storage tank to the Caro's acidreactor.

SUMMARY OF THE INVENTION

We have now found a process for producing Caro's acid by reactingsulfuric acid having a concentration of at least about 85% by weight andhydrogen peroxide having a concentration of at least about 50% byweight, wherein the hydrogen peroxide is introduced through a first feedline and the sulfuric acid is introduced through a second feed line intoa funneling zone open to the atmosphere, the first feed line and secondfeed line having air gaps between their ends and the funneling zone,passing said hydrogen peroxide and sulfuric acid by gravity flow fromsaid funneling zone into one end of a reaction zone that has been sizedto permit a pressure drop therein which is at least 8 times thetheoretical pressure drop for liquids flowing through such reaction zoneand removing a mixture containing Caro's acid from an exit end of thereaction zone.

DRAWINGS

In the drawings, FIG. 1 is a flow sheet showing the present process forproducing Caro's acid. FIG. 2 is a graph showing the theoreticalpressure drop in pounds per square inch through a given static reactorat various total flow rates as compared with the actual results obtainedby measuring the pressure drop against the same total flow rate measuredin gallons per minute.

DETAILED DESCRIPTION OF THE INVENTION

In carrying out the present process, the Caro's acid is produced byreacting sulfuric acid and hydrogen peroxide together, preferably in acontinuous manner, by adding these reactants into a funneling zoneopened to the atmosphere and then allowing the hydrogen peroxide andsulfuric acid to flow from the funneling zone by gravity into one end ofa reaction zone where the reaction takes place. The feed lines conveyingthe sulfuric acid and the hydrogen peroxide to the funneling zone haveair gaps between the ends of these lines and the top of the funnelingzone so that none of the reactants can overflow and enter into the feedlines of either the hydrogen peroxide and/or sulfuric acid. The reactionzone located downstream from the funneling zone into which the reactantsfrom the funneling zone are passed is preferably a pipe-like or tubereactor, whose diameter may be variable or constant, which may be eithervertically oriented, horizontally oriented or any skew angleintermediate these two extremes and is fed by gravity from the funnelingzone. Further, the reaction zone must have a size which permits apressure drop in the zone which is at least 8 times the theoreticalpressure drop for liquids passing through such reaction zone. Suchreaction zones are normally static reactors containing several mixingelements which ensure a complete mixing and reaction of the tworeactants.

The sulfuric acid can be of any concentration from about 85% by weightto up to about 98% by weight H₂ SO₄ with about 93% weight percentsulfuric acid being preferred because of its ready availability andworkability. Hydrogen peroxide can be of any concentration from about50% weight percent H₂ O₂ to about 90% weight percent H₂ O₂ with 70%weight percent hydrogen peroxide preferred because of safetyconsideration and because the lower amount of water in the 70 weightpercent hydrogen peroxide is desirable in this system. The mole ratiosof sulfuric acid to hydrogen peroxide (H₂ SO₄ /H₂ O₂) can range fromabout 1/1 to about 3/1 with about 2/1 to about 2.5/1 being preferred.The reaction results in Caro's acid being formed in a solution which isan equilibrium mixture of hydrogen peroxide, sulfuric acid, Caro's acidand water. The equation for this reaction is set forth below:

    H.sub.2 SO.sub.4 +H.sub.2 O.sub.2 ⃡H.sub.2 SO.sub.5 +H.sub.2 O

In this reaction, the presence of water in the reaction mixture isundesirable since it acts to inhibit formation of H₂ SO₅ and tohydrolyze the resulting H₂ SO₅ back into H₂ SO₄ and H₂ O₂. For thisreason, it is desired to minimize the presence of water by usingconcentrated sulfuric acid and concentrated hydrogen peroxide toincrease the yield of Caro's acid. Further, since sulfuric acid is avery strong dehydrating agent, it is desired to employ excess amounts ofsulfuric acid relative to the water formed in the reaction so that ittakes up the water as a hydrate and prevents it from inhibiting theCaro's acid formation in the reaction. However, use of extremely largeamounts of sulfuric acid is wasteful since the additional amounts ofCaro's acid formed is not commensurate with the cost of the excesssulfuric acid required to obtain the somewhat higher amounts of Caro'sacid formed. For these reasons, the optimum ratio for producing Caro'sacid commensurate with economical amounts of sulfuric acid employed isobtained when the mole ratio of H₂ SO₄ /H₂ O₂ is about 2/1 to about2.5/1. A typical composition prepared from a 2.5/1 mole ratio of 93weight percent sulfuric acid and 70 weight percent hydrogen peroxide isas follows: Caro's acid (peroxymonosulfuric acid) 25 weight percent;sulfuric acid 57 weight percent; hydrogen peroxide 3.5 weight percent;and water 14.5 weight percent.

In carrying out this reaction, we have found that the pressure generatedin the reaction zone does not drop off, at various flow rates throughthe reaction zone, as one would anticipate based on the theoreticalformula developed for typical static reaction zones. This is due to theaccelerated decomposition of the hydrogen peroxide reactant with releaseof voluminous gases to an extent much greater than would have beenpredicted for such reaction. In most cases, the predicted pressure dropwas on the order of 1/8 of the actual pressure drop obtained duringtesting and in many cases the predicted pressure drop was only 1/10 ofthat actually obtained in actual testing of these static reactors.

In the preferred embodiment, the funneling zone empties by gravity intoan essentially vertical, pipe-like, static reactor containing 3 or 4static mixing elements, such as those manufactured by Koch EngineeringCompany, and designated as SMV^(R) static mixers. These static reactorsare advantageous because they result in almost instantaneous reaction,have little hold up, operate in a continuous manner and need nomechanical or moving mixing devices to obtain complete mixing andreaction to form Caro's acid. The minimal hold up reduces decomposition,heat and pressure buildup and generally avoids run away reactions. Thedesign is such that the funneling vessel freely drains into the staticreactor and the static reactor is of sufficient diameter so that littleor no hold up exists in the funneling vessel, i.e., the reactantsessentially immediately contact the static mixing elements and mix withlittle or no solution being held up in the funneling zone. Little or nohold up in the funneling vessel is desirable in order to avoid prolongedresidence times and uncontrolled and unwanted variations in H₂ SO₄ /H₂O₂ mole ratios. Both of these factors, namely prolonged residence timesand unwanted H₂ SO₄ /H₂ O₂ mole ratios have the potential for causing athermal run away.

In carrying out the present process, the funneling zone is always keptopen to the atmosphere to prevent any possible build up of pressurecaused by the release of gases during the reaction to form Caro's acid.The absence of any possible pressure build up assures that the reactionmixture can never be forced back up the funneling zone and be propelledup into the tubes supplying either the hydrogen peroxide or sulfuricacid to the funneling zone. In the event of an excessive surge of gases,the reactants in the funneling zone can rise and even overflow the endsof the funneling zone without contaminating the ends of the feed tubessupplying the hydrogen peroxide and sulfuric acid because of the air gapwhich is always maintained between the end of these tubes and thebeginning of the funneling zone. The funneling zone can be formed from asimple funnel shaped unit to assure that both the peroxide and sulfuricacid are added together into the reaction zone where they mix and reactto form the Caro's acid. Although not necessary, it is often helpful ifthe top of the funneling zone has an overflow tube installed to drainany possible overflow of reactants so the overflow liquid can flow outof the funneling zone through a down spout and be combined with theCaro's acid removed from the reaction zone.

In carrying out the present process, the funneling zone and the reactionzone each have one end with direct access to the atmosphere and are thusunable to have any pressure build ups. The design is such that themaximum hydrostatic head which accumulates in the funneling zone ismaintained very low, not above about 2 to 4 inches of liquid to preventbuild up of reactants in the zone. The hold up of much more than thisamount of liquid represents a potential for an accelerating ratedecomposition in the entire mass of solution. To avoid this serioussafety concern, the static reactor is designed to have a diameter whichwill limit the hydrostatic head, maintain the solution hold up in thereactor within acceptable limits, and avoid accumulating large amountsof reactants in the funneling zone with the potential for a run awayreaction. The use of gravity feed into the reaction zone from thefunneling zone also assures maintaining the hydrostatic head in thefunneling zone within desirable limits. The use of pumps to feed themixture from the funneling zone into an undersized reaction zone underpressure is undesirable since a pump failure may result in an overlyexothermic and uncontrolled reaction leading to an increased hydrostatichead being built up in the funneling zone. By operating as describedabove, the Caro's acid is formed essentially on a continuous basis inthe reaction zone without pressure build ups and without excessivehydrostatic heads in the funneling zone and therefore without largeamounts of hot Caro's acid backing up into the funneling zone whichleads to possible uncontrolled and run away reactions of the hot Caro'sacid. A key element in achieving these ends is of course sizing thereaction zone so that the pressure drop across the reaction zone is atleast 8 times the theoretical pressure drop for liquids through suchreaction zones. This can assure that the pressure drop across thereaction zone results in a maximum hydrostatic head in the funnelingzone of no more than a few inches, which is acceptable. If the reactionzone were based on the theoretical calculations for such pressure drop,the hydrostatic head would be unacceptably larger and would pose asafety hazard because of the large amount of hot decomposing Caro's acidsolution backing up into the funneling zone.

The invention will now be described with reference to the drawings. InFIG. 1, the hydrogen peroxide is maintained in a storage tank 1 andpassed via line 3 into pump 5 which pumps the liquid through line 7 intothe funneling zone 17. In similar fashion, the sulfuric acid ismaintained in storage tank 9 and is passed through line 11 into pump 13where the sulfuric acid is pumped through line 15 into the top of thefunneling unit 17. The use of pumps 5 and 13 are optional since thereactants can also be passed by gravity into the top of the funnelingzone when pumping means are not required.

In either case, rate controllers are normally used in these lines toassure that the mole ratio of sulfuric acid to hydrogen peroxide iswithin the range of 1/1 to about 3/1 with 2/1 to about 2.5/1 beingpreferred. The ends of lines 7 and 15 are located above the top of thefunneling zone 17 to assure that an air space always remains between theends of these lines and the funneling zone. This air space is necessaryto assure that if the reactants overflow the top of the funneling zonenone of the reactants, hydrogen peroxide and sulfuric acid, will entereither line 7 or line 15 and cause contamination of any of the storagetanks.

The funneling zone 17 is in the form of a funnel and is designed topermit simultaneous adding of the reactants. The hold up of reactants inthis funneling zone is desired to be maintained as small as possible,for example, no more than about 2 to 4 inches in height to avoid thepotential for an accelerating rate decomposition. The top of thefunneling zone is always left open to the atmosphere to prevent anypressure build up. If desired, a loosely fitted dust cover may be placedover the top of the funnel with appropriate openings for the ends of thefeed lines 7 and 15. Dust covers serve to prevent unwanted particles andcontamination from entering into the funneling zone without forming apressure cap.

In addition, the funneling zone 17 normally is equipped with an overflow20. The overflow 20 is designed to remove any overflowing liquid fromthe funneling zone which accumulates above the hold-up liquid levelnormally obtained and to remove any such liquid from the funneling zonebefore it overflows the funneling zone 17. Any reagents which overflowand are removed via line 20 are then mixed with the Caro's acid mixtureremoved from the reaction zone.

The bottom of the funneling zone is connected to a static reactor 22.The initially added sulfuric acid and hydrogen peroxide in funnelingunit 17 are then passed by gravity into the static reactor 22 in orderto intimately mix these reactants to maximize conversion to Caro's acid.The pipe-like static reactor 22 has internal elements 24, usually 3 or4, to facilitate intimate mixing of hydrogen peroxide and sulfuric acid.The static reactor 22 is shown in a vertical orientation and this is thepreferred embodiment for carrying out this process. However, it ispossible to connect the static reactor to the funneling zone with acurved connection and have the static reactor either in a horizontal ordiagonal figuration. Whether the static reactor is oriented vertically,diagonally or horizontally, the gravity fed reactants from the funnelingzone 17 will flow into and intimately react in the static reactor 22 andbe converted to Caro's acid.

A typical static reactor is that produced by Koch Engineering Companycontaining four SMV^(R) elements for intimately mixing and reacting thefeed mixture to form Caro's acid. The exit 26 from the static reactor 22conveys the Caro's acid mixture formed in the static reactor, atatmospheric pressure, to the application where the Caro's acid is beingused. These include detoxification of cyanides and other well knownapplications for Caro's acid. The sizing of the static reactor 22 ismost important to this process since it must permit a pressure dropwhich is at least 8 times the theoretical pressure drop for liquidspassing through such reaction zones. This is reviewed in greater detailin the discussion of FIG. 2.

In FIG. 2, a graph is shown in which the horizontal axis is the totalflow rate, in gallons per minute, of a Caro's acid mixture (specificgravity 1.65) versus a vertical axis indicating the pressure drop inpounds per square inch (psi) across a typical Koch Engineering Companydesign 1.5 inch diameter SMV^(R) static reactor with four elements. Thebottom curve shows the theoretical or calculated pressure drop thatwould be expected from this static reactor based on the formula setforth in the Koch Bulletin KSM-6 issued in 1991. The upper curve showsthe actual pressure drop obtained. The formula for calculating thetheoretical pressure drop is as follows:

    .increment.P=0.0045(Q.sup.2 /D.sup.4)N(SG)

where .increment.P=pressure drop across the mixer, in psi

Q=flow rate of solution, gpm

D=diameter of element, inches

N=number of mixing elements

SG=specific gravity of the liquid

As will be seen from the graph, the calculated pressure drop across thestatic reactor varies from about 0 to a high of about 0.2 psi at a flowrate of from 1 to 6 gallons per minute. This is the theoretical orcalculated pressure drop based on the manufacturers empirical formula,given above, for his unit. In fact, when carrying out the presentreaction to form Caro's acid, we have found the actual, measuredpressure drop across this static reactor is shown in the upper curve. Aswill be seen from this upper curve when the flow rate is about 1 gallonper minute of Caro's acid mixture, the initial pressure drop across thestatic reactor is actually about 0.2 psi and unexpectedly climbs to ashigh as 1.7 psi at a flow rate of 6 gallons per minute of Caro's acidmixture.

In order to avoid this unexpected and greatly increased pressure drop,applicants' process sizes the static reactor to permit a pressure dropwhich is at least 8 times the theoretical pressure drop for liquids.That is, the size of the reactor is increased so that the pressure dropis reduced to at least 1/8 of the theoretical value for such staticreaction unit. The same principal can be applied to any static reactor;the theoretical pressure drop with the Koch Engineering Company reactoris used simply as a typical example of such static reactors.

The Caro's acid which is removed from the exit tube 6 of the staticreactor is fed to the application zone where the Caro's acid is used tocarry out conventional oxidation functions. The Caro's acid leaving thestatic reactor via exit tube 26 is open to the atmosphere and thus is atatmospheric pressure. It is not pumped or in any way put under anypressure when removed from the static reactor zone to avoid creatingback pressures in the static reactor. If, on occasion, there is a buildup of liquid overflowing the funneling zone 17 any excess liquid removedthrough overflow 20 is also flowed to the application zone along withthe regularly produced Caro's acid 28 from the exit pipe 26 of thestatic reactor 22.

Because of the poor stability of the Caro's acid thus formed at theelevated reaction temperatures, it is typical for the Caro's acid to beformed on site where it is to be used in the particular application. Inpractice, the Caro's acid thus formed is passed directly into the streamto be treated (for example, effluents where Caro's acid is used toreduce its cyanide concentration) without storing or transporting of thethus formed Caro's acid.

The following is an example which illustrates the use of the presentprocess.

An apparatus was set up as shown in FIG. 1 for the delivery of up to 5.5gallons per minute of Caro's acid solution. The funneling zone was inthe form of a funnel having an upper cylindrical section one foot indiameter by one foot high. A static reactor was installed in a verticalposition beneath the funnel so that liquid from the funneling zone wouldbe fed by gravity directly into the static reactor. The static reactorwas of tubular construction and was of a design by Koch EngineeringCompany that employed four SMV^(R) elements 3 inches in diameter. Thestatic reactor had a diameter of 3 inches and discharged into a 3-inchdiameter tube which delivered the generated Caro's acid solution to aprocess application. In this example, the sulfuric acid employed was 93%by weight H₂ SO₄ and the hydrogen peroxide employed was 70% by weight H₂O₂ and the mole ratio of H₂ SO₄ to H₂ O₂ was maintained at 2.5:1. At aproduction rate of 5.5 gallons per minute of Caro's acid the 3-inchdiameter static reactor gives a pressure drop across the static reactorof 0.097 psi and this gives a hydrostatic head in the funneling zone ofabout 1.6 inches, which is considered an acceptable hydrostatic head anda safe amount of solution hold up. The static reactor delivers a Caro'sacid solution at a rate of 5.5 gallons per minute from the staticreactor to an applications area for use as an oxidizing mixture.

ALTERNATE RUN

An alternate run was carried out using a static reactor that had adiameter of 1.5 inches and discharged into a 1.5 inch diameter tubewhich delivered the generated Caro's acid solution to process. The KochBulletin KSM-6 entitled "Status Mixing Technology" dated 1991 suggeststhe following formula for calculating pressure drop for a SMV^(R) typemixing element as follows:

    .increment.P=0.0045(Q.sup.2 /D.sup.4)N(SG)

where .increment.P=diameter drop across the mixer, in psi

Q=flow rate of solution, in gpm

D=diameter of element, inches

N=number of mixing elements

SG=specific gravity

Based on this formula, for the production of 5.5 gallons per minute ofCaro's acid solution with a static reactor of 1.5 inch diametercontaining four SMV^(R) mixing elements, it is calculated from the aboveequation using the following values:

Q=5.5 gpm

D=1.5 inches

N=4

SG=1.65 (adjusted for a temperature of 80° C.) that the pressure dropacross the static reactor would be about 0.18 psi. This would beequivalent to a hydrostatic height of about 3.0 inches of Caro's acid inthe funneling zone. Such a calculated value would be acceptable.However, when the reactants were introduced into the reactor inpractice, the hydrostatic drop across the static reactor was found to be1.55 psi and this results in a hydrostatic head, not of the abovecalculated 3.0 inches, but of approximately 26 inches. This is anentirely unacceptable amount of hot decomposing Caro's acid solutionwhich must be maintained in the funneling zone and represents a seriouspotential safety problem.

By using a static reactor as set forth in the above prior example of 3inches (instead of 1.5 inches) in diameter, the pressure drop across thestatic reactor was reduced to 0.097 psig (instead of 1.55 psig) and thisresults in a hydrostatic head being reduced from 26 inches (in the 1.5diameter static mixer) to about 1.6 inches (in the 3 inch diameterstatic mixer) which latter is an acceptable hydrostatic head andsolution hold up.

It is thus seen from the above that the pressure drop for the staticreactor in actual operation is entirely different from that obtained bytheoretical calculation using the above formula for calculating thepressure drop of the static reactor. This is because of the high amountof gas evolution, principally oxygen, which takes place when sulfuricacid and hydrogen peroxide react at high temperatures to form Caro'sacid. This was unknown prior to applicants' discovery of the extensivedifference between the theoretical or calculated pressure drop and theactual pressure drop obtained when carrying out the reaction. Bysuitably designing the static reactor, the pressure drop can bemaintained within acceptable limits and the hydrostatic head reduced toa point where the reagents hold up in the funneling zone can be broughtdown to an acceptable head of no more than about 2 to 4 inches.

We claim:
 1. A process for producing Caro's acid by reacting sulfuricacid having a concentration of at least about 85% by weight and hydrogenperoxide having a concentration of at least about 50% by weight, whereinthe hydrogen peroxide is introduced through a first feed line and thesulfuric acid is introduced through a second feed line into a funnelingzone open to the atmosphere, the first feed line and second feed linehaving air gaps between their ends and the funneling zone, passing saidhydrogen peroxide and sulfuric acid by gravity flow from said funnelingzone into one end of a reaction zone that has been sized to permit apressure drop therein which is at least 8 times the theoretical pressuredrop for liquids flowing through such reaction zone and removing amixture containing Caro's acid from an exit end of the reaction zone. 2.Process of claim 1 wherein the sulfuric acid has a concentration ofabout 85% to about 98% by weight H₂ SO₄.
 3. Process of claim 1 whereinthe sulfuric acid has a concentration of about 93% by weight H₂ SO₄. 4.Process of claim 1 wherein the hydrogen peroxide has a concentration ofabout 50% to about 90% by weight H₂ O₂.
 5. Process of claim 1 whereinthe hydrogen peroxide has a concentration of about 70% by weight H₂ O₂.6. Process of claim 1 wherein the mole ratio of H₂ SO₄ to H₂ O₂ employedis about 1:1 to about 3:1.
 7. Process of claim 1 wherein the mole ratioof H₂ SO₄ to H₂ O₂ employed is about 2:1 to about 2.5:1.
 8. Process ofclaim 1 wherein the reaction zone has a tube-like shape.
 9. Process ofclaim 8 wherein the reaction zone is a static reaction zone.
 10. Processof claim 9 wherein the static reaction zone has a plurality of internalelements to facilitate mixing.
 11. Process of claim 9 wherein the staticreaction zone is vertically oriented.
 12. Process of claim 1 wherein thefunneling zone is equipped with an overflow means for removing anyoverflowing reactants in the funneling zone from contacting the first orsecond feed lines.